A photomask is an opaque plate with holes or transparencies that allow light to pass through in a defined pattern. A photomask is commonly used in photolithography. The image for the photomask may originate from a computerized data file. For example, this data file may be converted to a series of polygons and written onto, e.g., a square fused quartz substrate covered with a layer of chrome using a photolithographic process. Lithographic photomasks are typically transparent fused silica blanks covered with a pattern defined with a chrome metal absorbing film.
In a photolithograhpic process, a set of photomasks, each defining a pattern layer in integrated circuit fabrication, is fed into a photolithography stepper or scanner and individually selected for exposure. More specifically, optical lithography, is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. Optical lithography uses light to transfer a geometric pattern from the photomask to a light-sensitive chemical photo resist (or “resist”) on the substrate. A series of chemical treatments then engraves the exposure pattern into the material underneath the photo resist. In complex integrated circuits, for example a modern CMOS, a wafer will go through the photolithographic cycle up to fifty times.
In order to create a photomask, a laser beam (laser writer) or a beam of electrons (e-beam writer) may be used to expose the photomask pattern defined in the data file by traveling over the surface of the photomask substrate in either a vector or raster scan manner. Where the photoresist on the photomask is exposed, the chrome can be etched away, leaving a clear path for the light in the stepper/scanner systems to travel through. Electron beam pattern generation offers advantages of resolution, corrections, and overall quality. However, e-beam writers are expensive and slow, which leads to increased costs for resulting photomasks.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.